Threaded fasteners are one of the most common mechanical fastening systems in use today. While bolts and nuts are typically the primary threaded fasteners, screws are just as common and important in the construction of mechanisms consumers use in multitudes of ways every day. A screw is used when, instead of a work piece being clamped between a nut and the head of the fastener, a portion of the work piece is internally threaded and the screw is torqued into the work piece itself. As with all threaded fasteners, screws torqued into engagement with an internally threaded work piece are subject to loosening over time and, as with threaded nuts and bolts, numerous devices have been incorporated to prevent such loosening. In the particular case of eyeglasses, the screws securing the temples and lenses often loosen followed by the undesired consequence of a temple falling off or a lens falling out.
The causes of such loosening in eyewear are varied. The repeated opening and closing of the temples by rotating the temple about the screw retaining it to the frame of the glasses will induce rotational loosening. Thermal gradients in the environment have a more pronounced effect on the female thread in which the screw is received than on the male threaded screw thus resulting in additional loosening forces. In other applications of screws being torqued into a work piece, vibration or dilation will also cause the screw to loosen over time. Often these screws are located in areas that are difficult to access, or may even be totally inaccessible to being retightened.
Prior attempts to overcome these loosening forces have included the addition of a smaller set screw, or locking screw, that is threaded through the side of the work piece into interfering perpendicular contact with the threads of the screw. However, a locking screw is subject to the same loosening forces as the primary screw and can be difficult and expensive to install. Additionally, in the case when the primary screw is relatively small, adding a set screw becomes impractical. Various types of liquid metal on metal glues have been utilized, but over time the effectiveness of these substances is questionable. Lock washers also have mixed success results.
Another problem encountered with machine screws not typically found with regular nuts and bolts is that a machine screw will often engage a greater number of threads in the work piece than in a standard nut of the same size, or in other cases, will require a screw of a significant threaded length necessitating numerous revolutions within the threads to reach a final torqued placement. Mechanical locking systems incorporating deformed threads to interferingly lock the fastener in place become disadvantageous in these circumstances. With long threaded fasteners or numerous internal threads engaged by the fastener, the significant number of turns required to finally torque the fastener will either totally defeat the deformation feature by the time final torqueing is accomplished or the extended sustained torqueing force applied to the fastener head will often damage the head making a final torqueing impossible and requiring an undesired replacement.
Thus, what is desired is a mechanism for quickly positioning and locking screws torqued into a threaded hole in a work piece and wherein the mechanism will reliably maintain the desired engagement of the screw in the receiving hole throughout the life of the apparatus on which it is installed.